In engine fuel delivery systems of current design, fuel is fed by a constant-delivery pump from a fuel tank to the engine, and excess fuel is returned from the engine to the fuel tank. Such return fuel carries engine heat to the fuel supply tank, and consequently increases temperature and vapor pressure at the fuel tank. Venting of excess vapor pressure to the atmosphere not only causes pollution problems, but also deleteriously affects fuel mileage. Excess fuel tank temperature can also cause vapor lock at the pump, particularly where fuel level is relatively low. Constant pump operation also increases energy consumption while decreasing both pump life and fuel filter life.
U.S. Pat. No. 4,649,884 discloses a fuel injection system for an internal combustion engine in which an electric-motor constant-delivery fuel pump supplies fuel under pressure from a tank to a fuel rail positioned on the engine. Excess fuel is returned to the supply tank through a pressure regulator as a function of pressure differential between the fuel rail and the engine air intake manifold. A plurality of fuel injectors are mounted between the fuel rail and the engine air manifold, with the injector nozzles being positioned adjacent to the fuel/air intake ports of the individual engine cylinders. U.S. Pat. No. 4,789,308, discloses a fuel delivery system for an internal combustion engine in which outlet pressure of an electric-motor fuel pump is monitored, and pump motor current is controlled as a function of such outlet pressure. Although the fuel delivery systems disclosed in the noted patents address the aforementioned problems in current fuel delivery system designs, further improvements remain desirable.
Parent application Ser. No. 276,801, filed Nov. 28, 1988 and assigned to the assignee hereof, discloses a fuel delivery system for an internal combustion engine that includes a fuel supply having an electric-motor fuel pump responsive to application of electrical power for delivering fuel under pressure. An engine air intake manifold supplies combustion air to the various engine cylinders, and at least one fuel injector is connected between the fuel supply and the air manifold. Pressure sensor mechanisms, preferably in the form of an integral differential pressure sensor, are responsive to pressure at the fuel injector and at the engine air manifold for supplying an electrical signal that varies as a function of pressure differential therebetween. The electric-motor fuel pump is driven as a function of such pressure differential, preferably by an analog or digital pulse width modulation amplifier that applies pulsed d.c. power to the motor at constant frequency and at a duty cycle that varies as a function of the pressure differential signal. In this way, fuel pressure at the injector is automatically controlled so as to maintain a constant pressure differential across the injeotor between the fuel rail and the engine air intake manifold, reduce volume of circulating fuel and thus engine heat delivered to the fuel tank, and energize the fuel delivery pump as a function of fuel demand. A problem with the system described in the parent application lies in the fact that the pump control electronics is directly responsive to pressure at the injector, which can fluctuate significantly during normal operation. That is, fuel pressure at the injector is controlled directly by the pump. As a result, the control system is overly sensitive, with motor speed continuously being cycled and adjusted.
An object of the present invention is to provide a fuel delivery system that maintains constant pressure differential across the fuel delivery mechanism, such as a fuel injector, so that the quantity of fuel supplied for a given injector activation time remains substantially constant and independent of fluctuations in air intake manifold pressure. Another object of the invention is to provide a fuel delivery system of the described character that is economical to implement in mass production of automotive fuel delivery systems, for example, and is reliable over an extended vehicle lifetime. A further object of the present invention is to provide a fuel delivery system of the described character that achieves on-demand fuel delivery, and thus reduces energy consumption while increasing pump and fuel filter operating lifetimes. Yet another object of the invention is to provide a fuel delivery system of the described character that reduces delivery of engine heat to the fuel tank, and thus reduces problems associated with fuel vaporization as hereinabove discussed. A further object of the invention is to provide a fuel delivery system that implements electronic control of the fuel pump as a function of fuel requirements, and in which the control electronics is cooled by fuel circulating in the delivery system.